1. Field of the Invention
The present invention relates to controllers for automatic transmissions mounted on vehicles, and more particularly to improvements to such a controller which includes a split-type valve body in which a pressure adjusting valve and an electromagnetic valve are accommodated.
2. Background Art
One such conventional controller for an automatic transmission is disclosed, for example, in a published unexamined Japanese patent application 8-270779. In this controller for an automatic transmission, for example, a select lever and a manually operated valve are used to change an area of a spool valve on which a pressure of the hydraulic oil acts so as to correspond to an N- or P-range indicative of a non-travelling state or a D- or R-range indicative of a travelling state. Thus, for example in the non-travelling state, a load on the pump is reduced. A pressure control valve which controls the pressure of the hydraulic oil acting on frictionally engageable elements of the automatic transmission is composed of a pressure adjusting valve which adjusts an opening in the valve depending on a quantity of movement of its spool to change the pressure of the hydraulic oil, and an electromagnetic valve which outputs a pilot (output) pressure to the pressure adjusting valve such that the electromagnetic valve is generally duty-cycle controlled to adjust the fed hydraulic oil pressure. Both the valves are generally provided within a valve body provided in a lower portion of the automatic transmission.
Since a general valve body is required to contain a spool and other elements, it is often divided into an upper and a lower body half. In order to ensure the freedom of layout of elements of the valve, an accumulator which absorbs vibrations of the hydraulic oil pressure is provided between the spool valve and the electromagnetic valve with the electromagnetic valve, spool valve and accumulator being provided in the lower body half. In this case, it is found that when a hydraulic oil path is provided between the electromagnetic valve and the spool valve so as to extend through the upper half of the valve body to connect the two valves provided in the lower half of the valve body, the vibrations of the oil pressure are amplified and that response to the gear shift control is deteriorated.
The present invention has been made in view of those problems. It is therefore an object of the present invention to provide a controller for an automatic transmission capable of ensuring the freedom of layout of components thereof and avoiding amplification of vibrations of the oil pressure and a reduction in the response to the gear shift control.